Blair damaged ligaments in his side's 24-14 Magners League win over Llanelli Scarlets on Friday at Murrayfield, but a scan failed to reveal the extent of the injury and it needs further investigation.

"Until the investigations are complete it's too early to give an accurate prognosis," an Edinburgh spokesman told the BBC website.

Scotland's Six Nations campaign kicks off against England on February 3 and are already without back-up scrum-half, Chris Cusiter.

In a similar fate, the Borders scrum-half also damaged his shoulder whilst playing for his country in the November Test match against the Pacific Islanders.

Cusiter has been ruled out of action until the half-way stage of the Six Nations tournament.

Blair, who has won 37 caps for Scotland, was injured after 64 minutes against the Scarlets.

It was a bad week for the Blair family as the half-back's younger brother David injured his back while playing fly-half for Sale Sharks on Saturday.

Blair junior lasted just 38 minutes of his Premiership debut before leaving the field with his injury and has since been ruled out for eight weeks.

Meanwhile, Edinburgh captain Chris Paterson will be in rehab throughout this week after sustaining some soft tissue damage to his back during the same Magners League victory over the Scarlets.

The Scotland skipper should be available for selection for the Heineken Cup match against Leinster at Donnybrook on Saturday.